Alzheimer's disease is associated with the deposition of amyloid in the brain during aging. Since the correlation between amyloid formation and AD was originally made, it has been recognized that there are many subtypes and forms that the disease can take. For example, accumulation of the amyloid ?-protein (A?) in the brain parenchyma is the hallmark of Alzheimer's disease (AD). Nevertheless, there is a poor understanding as to why amyloid forms, and it is not known whether there are unique structural motifs that promote the distinct pathological consequences leading to dementia. The focus of this proposal is to fill this critical void in knowledge. Accordingly, the overall hypothesis of this proposal is that the A? peptides forming amyloid with distinct subtypes have distinct structures that determine their location and pathology. To address this hypothesis we propose two specific aims. First, we plan to isolate amyloid from different subtypes of post mortem brain tissue of late-onset AD and early- onset familial AD. We plan to compare five different amyloid plaque subtypes: typical AD, atypical AD, cotton wool, early-onset AD (EOAD) and very early-onset AD (VEOAD). The last two subtypes are associated with familial AD mutations. Clinical information is available concerning age and gender, age of onset and duration of disease, course and symptoms of the disease, medication and ApoE genotype. In the EOAD and VEOAD cases genetic testing was performed for APP, PSEN 1, PSEN2 and tau. For most cases, biomarkers in CSF and neuroimaging results are available. The isolated amyloid will serve as seeds to nucleate fibril growth for in vitro studies. The structure and polymorphism of the fibrils will be assessed by complementary structural approaches including solid-state NMR spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and atomic force microscopy. Using the amyloid isolated from the five different subtypes of AD, we will assess the biofunctional consequences of the different strains using three approaches. First, we will assess the differences in the inflammatory response and cell toxicity due to different fibril forms using microglial cell cultures. Second, we will determine the influence of amyloid strains on promoting neuroinflammation. Third, we will determine the influence of amyloid strains on assembly and propagation in rat brain. The overall objective is to correlate pathologies (biofunctional consequences) of different amyloid subtypes between cell culture, rat brain and human brain, and to relate these pathologies with specific structural characteristics of the A? fibrils that are associated with the isolated amyloid from each subtype.